A mechanical inexsufflation device employs a ventilator for generating airflow under positive pressure, a first airflow channel connected to the ventilator, a first gate operative to selectively open or obstruct airflow through the first airflow channel, and a source of negative pressure airflow. The source of negative pressure gas flow may generate negative pressure simultaneously with the generation of airflow under positive pressure by the ventilator. A second gas flow channel connected to the source of negative pressure gas includes a second gate that may selectively open or obstruct gas flow through the second gas flow channel. A control unit operates to open or close the first and second gates in a mutually reciprocal and opposite manner. A patient interface unit conducts airflow to and from a patient's lungs according to the settings of the gates.
